# Thread: O.T. "Universal" Motors DC Voltage Question

1. Senior Member
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Let me clarify it's 10,000 watt continuous 18,000 surge. I use 2/0 welding cable to the batteries which are close. You don't need that size to run that winch. A 2000 watt is plenty if it runs off a wall 120v wall recept. I just a 2000 for \$50. Use a quick connect like on a snow plow leave the invereter behind the seat in a bag. & you always have 120v power for tools winches,etc without the hassle of a generator.

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I like the high voltage alternate alternator idea.

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Going from memory here, but if it's correct, the procedure was to tie the field winding directly to the output. In that case, the higher current in the field (the rotor) would induce a higher voltage in the output windings. Because the windings feed rectifiers which connect to a common bus, the output is dc with a 3 ph waveform riding on it.

When I look at this, it seems like there would be an awful lot of power being dissipated in the rotor. Normally you have about 3 amps in the rotor, with 14 or so volts driving it. If that voltage bumped up to say 42 volts, you would then have 9 amps in the field winding. Bump up the voltage to 84 (using these figures just for convenient math) the rotor current goes up to 18 amps.

This works out to over 750 watts into the rotor, vs the 42 watts dissipated under normal conditions, with even that small amount dropping as the regulator calls for less output from the alternator.

From this, I'm guessing that a conversion kit would include either a resistor to limit the rotor current, or a regulator circuit. It's also possible that the kit would simply be using battery voltage to power the field, then alternator rpm to deliver the voltage depending on the load asked for by the power tool or whatever. The latter makes the most sense to me, but also you would have to realize that the battery does not get any charge while using the alternator in 'high voltage' mode.

This is either not a problem because you would likely be using high mode only intermittently, or it shows the case for adding an alternator and leaving the existing system alone.

Beyond this, if your power requirements for the winch are going to be in the 2000 watt range, it might make more sense to just use a 2000-3000 watt generator. It will use less gas than the vehicle engine and might make more sense if you also have other needs for 'regular' power at remote locations.

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Originally Posted by dfw5914
I like the high voltage alternate alternator idea.
Your call but it will limit you to using DC motors which are not common anymore & not be portable to other trucks.

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Originally Posted by flylo
Your call but it will limit you to using DC motors which are not common anymore & not be portable to other trucks.
Most universal motor power tools and universal motors will be happy on DC.

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It depends... many variable speed tools may not like DC at all.

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Not to argue but I just don't see many DC or universal stuff anymore & why hobble youself when an inverer is plug & play & run anything you can plug into the wall. I've set up several remote location off the grid systems with many sizes of inverters which are easy, maintanence free, quick & simple. And the cost has really come down. Like I mentioned I bought a 2K preowned but new for \$50. If I need a power tool open the hood clip on 2 cables to one of the batteries & I have 120V power.Why use a generator or add an altenator? Simple & quick but again my opinion only.
Last edited by flylo; 05-31-2012 at 08:31 PM.

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If you go the inverter route, you would likely be carrying it in the vehicle most of the time. Why not then mount it and wire it up to a main power switch- if you're going for convenient use of the winch, then you can just flick the switch and it's ready. You can keep the engine running if your use would be long enough to put a serious drain on the battery. Doesn't take long at 100 amps to kill it- and that only represents 1200 watts.

If you do keep the engine running, then be aware that the alternator is going to try to supply that 100 amps to get the battery voltage back up. More than a few minutes of that will stress it pretty good.

No free lunch.

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I have 2 batteries because it's a diesel & I leave the engine running with a large draw. If camping or low draw I don't. You can hard wire it but then it's not portable to other autos. I like those "anderson" tipe connectors that snap together like on electric forklifts or golf cars as you can plug in a winch, battery cables, inverter,etc.

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Yeabut... the question was how to get that truck winch operating and a modified alternator is one option and may be the easiest and cheapest depending upon what is under the bench already and engine room space.

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